Cross-linked articles and coatings of vinyl chloride polymers and process for their manufacture

ABSTRACT

A process for cross-linking a vinyl chloride polymer which comprises mixing a non-cross-linked vinyl chloride-silane copolymer with an acid catalyst and heating, if necessary. The compositions produced by this process are useful as coatings, fibers or sheets.

United States Patent [1 1 Buning et al.

[451 Aug. 28, 1973 Siegmund Frick, Troisdorf-Oberlar, both of Germany[73] Assignee: Dynamit Novel Aktiengesellschaft,

Troisdorf, Germany [22] Filed: Sept. 13, 1971 [21] Appl. No.: 180,149

[30] Foreign Application Priority Data Sept. 19, 1970 Germany P 20 46293.5

[52] U.S. Cl.260/46.5 R, 204/l59.l3, 260/465 UA, 260/465 P, 260/875 R,260/92.8 A, 260/827 [51] Int. Cl. C08f 11/04 [58] Field of Search260/875 R, 92.8 A, 260/465 R, 46.5 U, 46.5 P

[5 6] References Cited UNITED STATES PATENTS 3,423,376 l/l969 Gobran etal. 260/875 R 3,554,989 l/197l Stamm 260/928 A 3,629,214 12/1971 Buninget a1 260/875 R 3,402,205 9/1968 Gregory 260/610 3,558,669 1/1971Breslow 260/349 OTHER PUBLICATIONS Bevington et al., Journal of theChemical Society, Feb. 1949, pp. 482 to 485.

Primary Examiner-Donald El. Czaja Assistant Examiner-M. l. MarquisAttorney Burgess, Clinklage & Sprung [57] 0 ABSTRACT A process forcross-linking a vinyl chloride polymer which comprises mixing anon-cross-linked vinyl chloride-silane copolymer with an acid catalystand heating, if necessary. The compositions produced by this process areuseful as coatings, fibers or sheets.

9 Claims, No Drawings CROSS-LINKED ARTICLES AND COATINGS OF VINYLCHLORIDE POLYMERS AND PROCESS FOR THEIR MANUFACTURE BACKGROUND Theinvention is directed to the problem of improving the manufacture ofcross-linked manufactured goods and coatings of vinyl chloride polymersand of endowing such cross-linked products with superior qualities.

Molding compounds must be created which, after they have been formed,can be cross-linked by the selection of certain catalysts either at roomtemperature or at higher temperatures. Furthermore, it would bedesirable to obtain cross-linked articles characterized by particularcross-linking densities. The distribution of the cross-links in themolecule should therefore be predeterminable, not random as it has beenin the state of the art. In particular, it has hitherto been impossibleto see to it that all of the molecules in the vinyl chloride polymersparticipate in the cross-linking process.

SUMMARY These problems are solved by the process of the invention and bythe cross-linked products or coatings manufactured thereby.

The subject of the invention is a'process for the manufacture ofcross-linked articles and coatings of vinyl chloride polymers, in whichnon-cross-linked copolymers of 30 to 99.9 weight percent vinyl chlorideand 0.1 to weight percent of a silane of the general formula in which R,is a vinyl or allyl radical, R represents an alkoxy radical of one to 18carbon atoms, an aryloxy radical of six to 12 carbon atoms and anaralkoxy radical of 7 to 24 carbon atoms, and R and K, have the samemeaning as R, but at the same time can be alkyl radicals of one to 18carbon atoms, aryl radicals of six to 12 carbon atoms and aralkylradicals of seven to 24 carbon atoms, are uniformly mixed with an acidcatalyst and heating if necessary for cross-linking.

DESCRIPTION The non-cross-linked copolymers of vinyl chloride or vinylor allyl alkoxy silanes used according to the invention can be made bysuspension, precipitation or emulsion polymerization. The kind ofcopolymerization depends on the intended application and on thestructure of the silanes. The important thing is that no crosslinkedcopolymers develop either during the copolymerization or even duringstorage. For certain applica tions, small amounts of cross-linkedcomponents cause no trouble. For the purposes of the invention, verysuitable gel-free copolymers of vinyl chloride with vinyl trialkoxysilanes and, in certain cases, other comonomers which can becopolymerized with vinyl chloride, are obtained by polymerization insuspension or in solution with the use of percarbonates, if the formedcopolymer is kept by known means in the fluid state. This is possible,for example, by using as the stirring means ribbon mixers, planetarystirrers or even balls in a rolling autoclave. The process of themanufacture of these gel-free copolymers is the subject of the GermanPatent application No. P 20 46 118.1 of September 18, 1970, nowpublished as German Patent No. 20461 l8.

Examples of the vinyl or allyl alkoxy silanes which can be copolymerizedwith vinyl chloride in the stated quantities are vinyl triethoxy silane,vinyl tripropoxy silane, vinyl tributoxy silane, vinyl tri-tert.-butoxysilane, vinyl trimethoxy silane, vinyl trihexoxy silane, vinyl trinonoxysilane, allyl trimethoxy silane, allyl triethoxy silane, allyltripropoxy silane, allyl tributoxy silane, allyl trimonoxy silane, etc.

Other monomers can be copolymerized with the vinyl chloride-silanecopolymer. Examples of such monomers are vinyl esters, fumaric esters,maleic esters, itaconic esters, vinylidene chloride, acrylonitrile,methacrylonitrile, acrylates, vinyl fluoride, and oleflns, especiallyethylene or propylene. The syndiotactic copolymers prepared in thetemperature range from to +20C are superior to the atactic copolymersprepared at higher temperatures as starting products for the manufactureof cross-linked PVC fibers which are completely insoluble in solventsand are characterized by high tensile strengths, especially at elevatedtemperatures. Furthermore, especially good results are obtained withvinyl chloride-silane copolymers which contain 30 to 99.5 weight percentvinyl chloride and 0.5 to 10 weight percent of a silane of theabove-stated formula as comonomers.

The acid catalysts suitable for the purposes of the invention can bedivided into two groups. Type I acid catalysts, especially thephosphoric acids and the sulfonic acids, and also hydrogen halide acids,especially hydrochloric acid, are effective even at room temperature.

Type II acid catalysts are especially suitable for crosslinking atelevated temperature, i.e., especially for temperatures from to C. Theseinclude carboxylic acids and boric acids, and a number of compoundswhich are essentially neutral, such as peroxides, azo compounds andazides, which probably exercise their catalytic action by cleavinghydrochloric acid from the polyvinyl chloride. Light or high-energyradiation produce a similar action. Hypophosphorous acid and aromaticsulfonic acids assume a preferred position as regards the catalyticactivity of the catalysts of Type I which are active at roomtemperature.

For certain applications, it is advantageous to add the acid catalysts,i.e., the acids themselves or the acidforming or acid-cleavingsubstances, during the copolymerization, whereby a uniform distributionin the copolymer is achieved. Suitable for this purpose are catalystswhich are not active during the copolymerization and during storageafter the copolymerization, and which require an increase intemperature, such as the above-enumerated acid catalysts of type II, aswell as masked catalysts, such as coordination compounds, acid formingor cleaving compounds, such as lactones, esters, for example, boric acidesters, phosphoric acid esters, which are hydrolytically cleavable inacids.

A gel-free polymerization is a polymerization free of cross-linking andis performed without the addition of a solvent or diluent for themonomers or copolymer formed. This is a so-called mass or substancepolymerization which can also be carried out in the presence of awater-free solvent. During the polymerization the polymer particles andthe reactants are kept in a fluid state by means of a mixer or grinder.

A gel-free polymerization can be carried out in an aqueous medium orwith traces of water using any suitable polymerization method. This isalso required when the silane comonomer used is not hydrolyzable underthe polymerization conditions.

The acid catalyst is used in quantities of 0.1 to 5 percent, andpreferably 0.l to 1 percent, of the weight of the copolymer. The mixingof the non-cross-linked copolymer with acid catalyst is best performedin the presence of a solvent or swelling agent. Suitable solvents areparticularly ketones, especially cyclohexanone, and tetrahydrofuran. Incyclohexanone, the cross-linking reaction generally takes place morerapidly than in tetrahydrofuran. The cross-linking of solutions of thecopolymers by the Type 1 catalysts which are active at room temperatureevidences itself in a transformation of the fluid solution to a firm,jelly-like mass. At first mechanical vibrations, such as sound or shock,are absorbed by this jelly. This effect diminishes after a period oftime. This peculiar behavior clearly shows how different is theconstruction of the PVC types cross-linked in accordance with theinvention from the cross-linked PVC copolymers of the prior art. Thecause is apparently to be sought in the fact that the cross-linkingtakes place throughout the molding compound or throughout the objectshaped therefrom, in a virtually simultaneous and complete manner,because if the cross-linking structure of the molecules present in themolding compound is different, or if non-crosslinked molecules arepresent, the above-described effect does not take place.

If the mixing of the non-cross-linked copolymer with the acid catalystis performed in the presence of a plasticizer for the copolymer, themolding compound changes from a gel-like state to a powdered state whenit is kneaded at, for example, 160 to 180C, if catalysts of Type I areused.

The polyvinyl chloride cross-linked under these conditions appears toform with the plasticizer a coordination compound in which theplasticizer is no longer a jelling agent. a

The molding compounds prepared by the process of the invention offerspecial advantages for the production of cross-linked types of PVCfibers which are entirely insoluble in solvents. They have improvedtensile strengths, especially at higher temperatures. The filaments inthis case are made preferably from solutions, with the addition of theabove-mentioned mentioned catalysts-of Type I in such quantities thatthe crosslinking does not occur until during the spinning process, orafter it, e.g., during the stretching process. With the syndiotactictypes the stretching can also take place prior to the cross-linking.Syndiotactic vinyl chloride-silane copolymers are crystalline, and thecrystalline portions can be oriented by stretching. By the cross-linkingprocess of the invention, the crystalline portions can then becompletely fixed. Analogous statements can be made concerning themanufacture of sheets. For example, such a copolymer with theincorporated catalyst of Type I is spun as usual from a solution and thequantity of the catalyst can then be adjusted so that the fiber or sheetthat has been made cross-links by itself within a few hours. Nocomparably simple procedure giving similar results as regards resistanceto solvents and tensile strength has hitherto been possible with vinylchloride copolymers.

Solutions of the non-cross-linlted vinyl chloridesilane copolymers inketones or tetrahydrofurans or the like, which are used in accordancewith the invention are also usable to special advantage for themanufacture of PVC-base varnishes which are characterized by improvedsolvent resistance and improved thermal stability of shape as comparedwith the previously known PVC varnishes which set at room temperature.The pot life and setting conditions can be adjusted as desired by thenature and quantity of the acid catalyst of Type I that is used. Thecoatings made according to the invention have excellent characteristicsof adhesion to metals. in this case the catalyst appears to play animportant part. Especially good adhesion is achieved whenhypophosphorous acid is used.

The cross-linking cannot only be controlled very precisely by theselection of the catalyst and its concentration, and by the temperaturesapplied, but it is also possible for it to be controlled very simplywith the aid of infrared analysis. In the large-scale production ofcrosslinked products, especially fibers and sheets, and in theadaptation of PVC varnishes or coatings to a particular application,this, of course, if very important.

Controls of this kind have not been possible hitherto in thecross-linking of vinyl chloride polymers. The cross-linking process ischaracterized by a definite recession of one band in the infrared atapprox. 1080 cm, and by the development of a new band at approx. 1025cm. At the same time, a band occurs at 3580-3600 cm", which is connectedwith an unassociated OH vibration of an SiOH group. This constitutes apossibility for modification which has hitherto been unknown in PVC.

Cross-linked products made according to the present invention, such asfibers and sheets, are characterized by antistatic behavior, dependingon the application and the nature of the catalyst. The treatment offibers of thepresent invention with antistatic agents is thuseliminated. The antistatic feature cannot be washed out.

The cross-linked products or coatings made in accordance with thepresent invention are characterized by structural units for the formulain which y is 0m 1 and R and R represent an alkoxy radical with one to18 carbon atoms, an aryloxy radical of six to 12 carbon atoms, anaralkoxy radical of seven to 24 carbon atoms, alkyl radicals with one to18 carbon atoms, aryl radicals of six to 12 carbon atoms, aralkylradicals of seven to 24 carbon atoms, or hydroxyl groups.

EXAMPLES 1 to 12 A percent solution of a copolymer of 95 weight percentvinyl chloride and 5 weight percent vinyl tripropoxysilane of a K valueof 65 in tetrahydrofuran is combined with various amounts of the acidcatalysts listed in Table 1. In the results shown, Hardening Time Irepresents the time within which plain gelification occurs, andHardening Time II is the time at which the gel absorbs virtually nomechanical vibrations.

EXAMPLE 13 Example 9 is repeated, except that cyclohexanone is used asthe solvent instead of tetrahydrofuran. In this case, Hardening Time Iis 1% hours and Hardening Time II is 8 hours, i.e., in cyclohexanone thereaction takes place more rapidly. I

EXAMPLES 14 to 27 A 15 percent solution of the non-cross-linked vinylchloride-silane copolymer used in the preceding examples was prepared intetrahydrofuran and, after dispersing the catalyst uniformly into thesolution, sheets were cast with a thickness of about microns; Todetermine the degree of cross-linking, weighed amounts of the sheetswere refluxed in trichloroethylene for eights hours and then refluxed inmethanol for eight hours, and dried. The weight loss is an index of thecrosslinking: the lower it is, the higher is the degree of crosslinkingand the greater is the number of molecules that have taken part in thecross-linking process. The results are summarized in Table 2.

Table 2 Trichloro- Example Catalyst Quantity ethylene test Temp.

1n wt-% of wL loss "C 14 None 38.5 20 15 Phosphoric acid 0.5 5.04 20 16Phosphoric acid 0.5 0.0 100 17 Phosphoric acid 0.1 7.7 20 18 Phosphoricacid 0.1 0.1 100 19 Hypophosphorous 0.1 0.0 20

acid 20 0.1 0.0 100 21 Phosphoric acid 1.0 0.0 M 22 Benzoic acid 1.035.0 20 23 Boric acid 1.0 12.8 20 24 Boric acid 0.5 0.0 100 25Trichloroacetic 1.0 22.2 20

acid

26 1.0 6.3 100 27 Toluenesulfonic 1.0 0.0 20

acid (monohydrate) According to the infrared analysis, too, the degreeof crossdinking, i.e., the number of cross-linking points, is

greatest in the Examples in which hypophosphorous acid andtoluene-sulfonic acid are used.

EXAMPLES 28 to 42 48 Grams of the copolymers of 95 weight percent vinylchloride and 5 weight percent vinyl triethoxysilane, 32 grams ofphthalic acid diisooctyl ester, 1.6 grams of dibutyl tin mercaptide (TinStabilizer 17 M) and 240 milligrams of the catalyst listed in the tablewere placed in the ccm cam chamber of a Brabender PLASTICORDER. Thechamber was heated to 180C and the cam roll was rotated at 27 rpm. Atcertain intervals of time samples were taken and the amount ofcross-linking was determined by boiling in tetrahydrofuran, theinsoluble material remaining undissolved.

TABLE 3 Time Percentage Example Min. Cross-Linked Catalyst 28 l 0Chloroacetic acid 29 5 0 30 10 20 31 15 80 32 20 100 33 l 80Hypophosphorous acid 34 2 100 35 l 0 Boric acid 36 l0 0 37 15 10 38 3039 l 0 Dicumyl peroxide 40 5 0 41 20 40 42 30 Similar results areobtained with copolymers which contain vinyl trimethoxy, vinyltributoxy, vinyl tri-tbotuxy, vinyl tripentoxy and vinyl trihexoxysilane. As the carbon chain lengths of the alkoxy radical increase, sodo the cross-linking times.

EXAMPLES 43 to 48 Sheets 20 microns thick are cast from tetrahydrofuransolutions of copolymers of vinyl chloride with various contents of vinyltripropoxy silane, with the addition of 0.5 percent by weight (withreference to the copolymer) of hypophosphorous acid. The sheets are thenhardened in boiling water. Table 4 lists the tensile strengths at thevarious silane contents.

TABLE 4 Tensile Strength Tensile Strength '5 at 23,C in at 100C, ExampleSilane kp/em in kp/cm 43 0 550 15 44 1 510 30 45 2 500 50 46 3 490 65 474 470 80 43 5 450 What is claimed is:

1. Process for cross-linking vinyl chloride polymers which comprisesmixing:

a. a non-cross-linked vinyl chloride-silane copolymer containing 30 to99.9 weight percent vinyl chloride copolymerized with 0.1 to 20 weightpercent of a silane having the formula wherein R, is selected from thegroup of vinyl and allyl;

R, is selected from the group of alkoxy of one to 18 carbon atoms,aryloxy of six to 12 carbon atoms, and aralkoxy of seven to 24 carbonatoms; and

R and R are the same as R or are selected from the group of alkyl withone to 18 carbon atoms, aryl of six to 12 carbon atoms and aralkyl ofseven to 24 carbon atoms; with b. from 0.01 to percent of an acidcatalyst selected from the group consisting of i. a room temperaturecatalyst from the group consisting of a phosphoric acid, a sulfonicacids and a hydrogen halide acid; and

ii. an elevated temperature catalyst from the group consisting of acarboxylic acid, a boric acid and a compound that cleaves hydrochloricacid from the vinyl chloride copolymer from the group consisting of aperoxide, a lactone, an azo compound and an azide and c. heating attemperatures of from 100 to 180C when an elevated temperature catalystis used.

2. Process of claim 1 wherein the catalyst is hydrochloric acidgenerated by cleaving from the vinyl chloride copolymer by light orhigh-energy radiation.

3. Process of claim 1 wherein said vinyl chloridesilane copolymer iscopolymerized with other monomcrs selected from the group of vinylesters, fumaric esters, maleic esters, itaconic esters, vinylidenechloride, acrylonitrile, methacrylonitrile, acrylates, vinyl fluoride,and olefins.

4. Process of claim 1 wherein said copolymer contains 30 to 99.5 weightpercent vinyl chloride copolymerized with 0.5 to 10 weight percent ofsaid silanev 5. Process of claim 1 wherein the vinyl chloride silanecopolymer is syndiotactic.

6. Process of claim 1 wherein said mixing takes place in the presence ofa solvent or swelling agent.

7. Process of claim 1 wherein said mixing takes place in the presence ofa plasticizer for the polymer.

8. Composition comprising a uniformly cross-linked vinyl chloride-silanecopolymer containing 30 to 99.9 weight percent vinyl chloridecopolymerized with 0.1 to 20 weight percent silane and characterized bystructural units having the formula wherein R and R are defned in claim14 or are hydroxyl, and y is 0 or l.

9. Composition of claim 8 wherein the vinyl chloridesilane copolymer issyndiotactic.

2. Process of claim 1 wherein the catalyst is hydrochloric acidgenerated by cleaving from the vinyl chloride copolymer by light orhigh-energy radiation.
 3. Process of claim 1 wherein said vinylchloride-silane copolymer is copolymerized with other monomers selectedfrom the group of vinyl esters, fumaric esters, maleic esters, itaconicesters, vinylidene chloride, acrylonitrile, methacrylonitrile,acrylates, vinyl fluoride, and olefins.
 4. Process of claim 1 whereinsaid copolymer contains 30 to 99.5 weight percent vinyl chloridecopolymerized with 0.5 to 10 weight percent of said silane.
 5. Processof claim 1 wherein the vinyl chloride-silane copolymer is syndiotactic.6. Process of claim 1 wherein said mixing takes place in the presence ofa solvent or swelling agent.
 7. Process of claim 1 wherein said mixingtakes place in the presence of a plasticizer for the polymer. 8.Composition comprising a uniformly cross-linked vinyl chloride-silanecopolymer containing 30 to 99.9 weight percent vinyl chloridecopolymerized with 0.1 to 20 weight percent silane and characterized bystructural units having the formula
 9. Composition of claim 8 whereinthe vinyl chloride-silane copolymer is syndiotactic.